Thin ferroelectric films for thermal detector applications

The deposition of thin films of lead scandium tantalate (Pb(Sc1/2Ta1/2)O3 have been investigated by two processing routes, in the first, progress is reviewed for chemical vapour deposition in a purpose built low pressure reactor, utilising suitable modified proprietary precursors. Deposition has been studied over the temperature range 400–800°C and, in general, amorphous films result which convert to crystalline perovskites on subsequent annealing. However, inclusion of hydroxy compounds in the vapour train catalyses the crystallisation process and enhances the growth rate at above 600C. It was found that the best thin films, in terms of density and morphology, are formed at low deposition rates 1–2μm/hr. The perovskite phase is obtained if the gas phase composition is controlled throughout growth. The choice of precursors, gas compositions and growth conditions will be described. In the second process, lead scandium tantalate thin films (>1μm) were deposited using a modified sol-gel solution route. This was achieved by spin-coating a solution of metallo-organic compounds of scandium and tantalum followed by lead, onto suitable substrates and firing and annealing the films at 800–1000C. These firing temperatures gave films with grain sizes ranging from 0.5–4μm, which are single phase perovskite. Permittivity, dielectric loss and field induced pyroelectricity have been measured against field and temperature to assess the pyroelectric figure-of-merit, Fn of films obtained from both film deposition process. The FD for sol-derived films indicates a performance similar to that of bulk ceramic material.